Sampling Procedure
The sample for Iraq was selected using stratified random sampling. Three levels of stratification were used in this country: business sector, establishment size, and governorate.
Business sector stratification was defined by creating six levels: the universe was stratified into four manufacturing sub-sectors (food, non-metallic mineral products, and chemicals/rubber products) and an "other manufacturing" category, retail/wholesale, and an "other services" category.
Size stratification was defined by three levels following the standardized definition for the Enterprise Surveys: small (5 to 19 employees), medium (20 to 99 employees), and large (more than 99 employees). For stratification purposes, the number of employees was defined on the basis of reported permanent full-time workers.
Regional stratification was defined by 10 sub-national locations (governorates) in Iraq: Ninevah, Kirkuk, Baghdad, Babil, Kerbala, Al-Najaf, Thi-Qar, Basra, Suleimaniyah, and Arbil.
Iraq's Central Organization for Statistics (COSIT) with the cooperation of Kurdistan Regional Statistical Office (KRSO) provided the World Bank with a sampling frame, generated in 2009 during the initial discussions regarding Enterprise Surveys. However despite the target sample design of 1,000 firms (which was known to be extremely ambitious at the outset of the survey project), the list from COSIT contained 959 firms. Transportation, storage, and communications sectors (group I) along with the IT sector were missing in this sampling frame.
Given the missing sectors and below-target total of firms in the sample frame, the implementing contractor solicited and obtained lists of registered companies from local (governorate-level) chambers of commerce. The implementing contractor provided the World Bank with Excel sheets from seven governorates. 106 firms in sectors group I and ISIC 72 were randomly selected and appended to the list of 959 firms from COSIT. Thus a total of 1,065 firms constituted the sample frame provided to the implementing contractor.
Response Rate
The overall survey response rate was 92%.
The number of firm contacts per realized interview was 1.37. This number is the result of two factors: explicit refusals to participate in the survey, as reflected by the rate of rejection (which includes rejections of the screener and the main survey) and the quality of the sample frame, as represented by the presence of ineligible units. The number of rejections per contact was .06.
Item non-response was addressed by two strategies:
a- For sensitive questions that may generate negative reactions from the respondent, such as corruption or tax evasion, enumerators were instructed to collect the refusal to respond as a different option from don’t know (-7).
b- Establishments with incomplete information were re-contacted in order to complete this information, whenever necessary.
Survey non-response was addressed by maximizing efforts to contact establishments that were initially selected for interview. Attempts were made to contact the establishment for interview at different times/days of the week before a replacement establishment (with similar strata characteristics) was suggested for interview. Survey non-response did occur but substitutions were made in order to potentially achieve strata-specific goals.
Weighting
For some units it was impossible to determine eligibility because the contact was not successfully completed. Consequently, different assumptions as to their eligibility result in different universe cells' adjustments and in different sampling weights. Three sets of assumptions were considered:
a- Strict assumption: eligible establishments are only those for which it was possible to directly determine eligibility.
b- Median assumption: eligible establishments are those for which it was possible to directly determine eligibility and those that rejected the screener questionnaire or an answering machine or fax was the only response. Median weights are used for computing indicators on the www.enterprisesurveys.org website.
c- Weak assumption: in addition to the establishments included in points a and b, all establishments for which it was not possible to finalize a contact are assumed eligible. This includes establishments with dead or out of service phone lines, establishments that never answered the phone, and establishments with incorrect addresses for which it was impossible to find a new address. Note that under the weak assumption only observed non-eligible units are excluded from universe projections.
